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From "Segel, Mike" <mse...@navteq.com>
Subject RE: best way to replace disks on a small cluster
Date Wed, 07 Sep 2011 13:21:00 GMT

Ok, so you have a small cluster w raid drives...
First, raid isn't really a good idea.

You want to replace the old raid drives w new 2TB drives in JBOD.
(Which is better.)

What percentage of your drives are filled?
Assuming you have enough space on 2 of your DNs, you can decommission one, run fsck and balancer
to compensate for the lost blocks, then rebuild your node.
Replace the drives w the 2TB as JBOD drives, bring the node back up.
Rebalance the cluster to get more of the data on the machine, and repeat the process for the
other nodes.



From: Marco Cadetg [marco@zattoo.com]
Sent: Wednesday, September 07, 2011 8:19 AM
To: general@hadoop.apache.org
Subject: best way to replace disks on a small cluster

Hi there,

Current situation:
3 slaves with each two 320GB disks in RAID 1. All the disks show high read
errors and io throughput has gone below 5Mb/s without running any hadoop
job. (It looks like it will fall apart soon...)

What is the best way to replace the bad disks? I may be able to add another
two machines into the mix. I can't / won't rebuild the RAID as my new disks
will be 2TB each, so I wouldn't like to use only 320GB of them.

Is the best way to add two new nodes into the mix and then mark two other
machines to dfs.host.exclude. And after some time I can take them out???

Thanks for your help,

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